PROJECT SUMMARY The role of flavors added to tobacco products remains debatable in tobacco regulatory research. From a harm reduction perspective, flavors may help cigarette smokers make the switch to potentially less harmful tobacco products. At the same time, flavored non-combustible tobacco products may serve as a precursor to cigarette smoking, and they are particularly attractive to youth and young adults who otherwise may not smoke. Flavor bans have been under discussion over years and have been recently heightened. In June 2018, San Francisco approved a ban on menthol cigarettes and flavored electronic cigarettes. This ban has the potential to spark a national trend. To support the evidence-based decision-making of FDA and policy change at the national level, vigorous research on the impact of flavor bans are needed. The aim of this study is to examine the impact of two major flavor ban alternatives on young adults who are users of tobacco/electronic nicotine delivery systems. We will assess the empirical change in tobacco use in San Francisco, CA where flavor bans have been implemented (Aim 1) and estimate the reaction patterns to flavor bans in a city where the policy has NOT been implemented using discrete choice experiments (DCEs) (Aim 2). Afterwards, we will develop an agent-based model (ABM) with the result from DCEs (Aim 2) serving as the core behavior pattern at the individual-level, and empirical patterns at the population-level (Aim 1) serving for the ABM's assessment. As a bottom-up approach, the ABM can examine various flavor ban policies in both cities (Aim 3). Combining empirical results, estimations from hypothetical experiments, and simulations of various flavor bans' scenarios in various contexts, the evidence and insights generated from the proposed study will allow researchers to explore the implications of a flavor ban policy on a given environment. Results may also be extrapolated to the United States at large.